Most electronic equipment produced today incorporates one or more printed circuit boards, each having electronic components mounted thereon. The mounting of components on the printed circuit board is usually accomplished automatically by machines constructed for this purpose. Machines for mounting components to printed circuit boards are known in the art and are available from a number of commercial vendors. While the structural details of such machines vary, each typically includes a stage for supporting a printed circuit board thereon in registration with a mechanism for placing components on the circuit board. In practice, the stage carries two or more machanisms for engaging the circuit board to fix the location thereof on the stage a set distance from the component placement mechanism.
In order for a component mounting machine to achieve high circuit board throughput, the mechanisms theron for engaging the circuit board must be capable of rapid and reliable operation. Further, the circuit board engagement mechanisms must be capable of rigidly holding the circuit board in place to avoid shifting thereof during the placement of components thereon. Shifting of the circuit board on the stage can cause misplacement of components. This problem is especially critical when components such as chip carriers are placed with the leads therof in contact with bonding pads on the circuit board. In some instances the spacing between chip carrier leads is as small as 0.025 inches so even very small shifts in the position of the circuit board can result in misalignment of the leads with the bonding pads on the circuit board.
In the past, mechanisms for engaging a circuit board have typically included a pin which is dimensioned for receipt in a tooling hole located adjacent to the edge of the circuit board. The pin is rigidly affixed to a shaft of an actuator, such as a fluid cylinder or electrically operated solenoid fixedly carried by the stage. In order for the engaging mechanism to fix the location of the circuit board on the stage, the circuit board is first indexed to align the tooling hole therein in registration with the pin. The actuator is then energized to insert the pin into the tooling hole and thereby capture the printed circuit board.
The rigidity of the pin may cause it to become wedged or stuck in the tooling hole when rapidly inserted therein if the tooling hole is misaligned with the pin. Such misalignment may arise because of variations in the location of the tooling hole in the circuit board caused by manufacturing tolerances. The wedging and sticking problem can be reduced by increasing the diameter of the tooling holes. However, increasing the diameter of the tooling holes reduces the area on the circuit board that can be occupied by components, which is undesirable. Moreover, increasing the size of the tooling holes can lead to increased play between the circuit board and each of the pins, thereby resulting in possible misplacement of components on the circuit board.
Accordingly, there is a need for a technique for rapidly and accurately engaging a substrate, such as a circuit board, to hold it in place.